This invention relates to an ultrafine-crystalline alloy excellent in soft magnetic properties and corrosion resistance.
Silicon steel, Fe-Si alloys, amorphous alloys, etc. are well known as soft magnetic materials, and their important properties are high relative permeability .mu. and saturation magnetic flux density Bs.
In addition to magnetic properties, corrosion resistance is an important property since these magnetic materials would be used under various circumstances.
However, it had been considered difficult to achieve both high saturation magnetic flux density Bs and high relative permeability .mu. at a time in the magnetic materials. Fe-based amorphous alloys have, for example, high saturation magnetic flux density Bs, while they are inferior to Co-based amorphous alloys in soft magnetic properties. On the other hand, the Co-based amorphous alloys are excellent in soft magnetic properties, while they do not have sufficient saturation magnetic flux density Bs.
High saturation magnetic flux density Bs and high relative permeability .mu. had conventionally been thought incompatible. U.S. Pat. No. 4,881,989 discloses an Fe-based soft magnetic alloy with ultrafine crystal grains having both high saturation magnetic flux density Bs and high relative permeability .mu.. This Fe-based alloy having an average grain size of 500 .ANG. or less is produced through a crystallization process after it is quenched rapidly into an amorphous state. This Fe-based alloy with ultrafine crystal grains has good corrosion resistance to some extent because it contains Nb, etc. The corrosion resistance of this Fe-based alloy, however, may not be sufficient depending on surroundings in which it is used.